I love the satisfying sound effect that triggers after clicking Check and getting a problem right (the new confetti visual effect was also a fun touch).

I also love the sound effect that triggers whenever you learn a new skill (in the Level bar).

However, these two sound effects now trigger at the same time, and I find the combination of them both going off at once to be rather audibly jarring. I might be the only one who feels that way, but Feedback is Feedback, so I just thought I'd mention it =)